The present disclosure relates to the use of one or more ion beams to prepare materials for microscopic observation or spectroscopic analysis. Microscopic observational techniques include, but are not limited to, optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and reflection electron microscopy (REM). Spectroscopic analysis techniques include, but are not limited to, x-ray micro-analysis, reflection electron energy-loss spectroscopy (REELS), electron back-scattered diffraction (EBSD), x-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Materials to be viewed under any microscopic technique may require processing to produce a sample suitable for microscopic examination.
Transmission electron microscopy (TEM) is an important technique for studying the detailed microstructure of many materials. The preparation of samples for atomic resolution TEM is very demanding, requiring a final sample that is very thin (i.e. <50 nanometers) and free from artifacts. Typically, sample preparation involves initial slicing, sectioning, and mechanical thinning to produce a relatively thin (i.e. 100-200 micrometers) disk of sample material. Ion beam milling of the sample may then be employed to further thin, smooth, and expose regions of interest in the sample for later TEM study, typically producing a sample with a thickness of 50 nanometers.
Ion beam milling of a material can produce samples that are well suited for microscopic examination. An ion beam irradiating device may generate, accelerate, and direct a beam of ions toward a sample. The impact of ions on the sample will sputter material away from the area of ion impact. Furthermore, the sample surface may be polished by the ion beam to a substantially smooth condition, further enhancing observational properties of the sample. Regions of interest in the sample may be exposed and polished by the use of ion beams, thus making a suitable observational sample from the material under investigation.
Ion beam systems used to mill samples destined for TEM analysis typically expose an interface or produce a sample with an electron transparent region. Many of these systems have rotating samples and fixed beams, so that the beams may strike the sample from multiple directions. This provides for more uniform milling of a sample by compensating for the shadowing of certain regions that may happen due to the nonuniform topology of the sample surface. In the typical system used for ion beam milling, material is removed most quickly from the sample by the ion beam in the region of the sample described by the intersection of the rotation axis of the sample with the center of the ion beam itself. It is often difficult to position a sample in the ion beam system so that the specific region of interest lies at the center of rotation. Some amount of trial and error may be expected when trying to target a specific region of interest in the ion beam sample preparation process.
Important considerations to users of the ion beam milling technique include: reducing or minimizing the time and effort the user is occupied in processing the sample; reducing or minimizing the number of steps where delicate samples are directly handled and at risk for damage, such as during mounting to sample holders for processing or analysis; reducing or minimizing the time and effort the user is occupied transferring the sample into the ultimate analysis equipment (imaging or spectroscopy), and aligning the coordinates of the prepared sample region to the ultimate analysis equipment prior to analysis; ensuring high quality and high probability of success in processing and imaging the sample; reducing or minimizing the time that the ion milling equipment and sample mounting equipment are occupied for each sample; and ensuring high-quality microscopy observation of the sample during sample mounting and ultimate analysis by reducing the working distance required between the sample and the objective or probe-forming lens used for observation.
In consideration of the foregoing points, it is clear that embodiments of the present disclosure confer numerous advantages and are therefore highly desirable.